Core chucks 10, FIG. 1, for use in winding and/or unwinding rolls of material including but not limited to paper, plastic film and metal foil (not shown) are well known. Core chucks 10 typically include, in addition to other mechanical elements, a mounting plate 12 having a plurality of holes 14, keyway and/or other connecting features adapted for mounting to the rotating surface of the winding or unwinding machine, often but not necessarily known as a roll stand (not shown). The structure of torque activated core chucks also generally includes a central cam 16 having a multi-faceted surface 18 and an end cap 20. The mounting plate 12 often includes an inwardly, cylindrical opening (often termed a pilot hole) 24 disposed in the center of the mounting plate 12 which is adapted to receive the first end 22, often termed a pilot, of the central cam 16. The first end 22 of the central cam 16 is generally made cylindrical (typically using a lathe) such that the end 22 fits, with controlled clearance or interference, within the opening 24 in the mounting plate 12. This is done for geometric (centering) and/or load carrying reasons. The shape of the pilot engagement (round) tends to facilitate economical manufacturing such as by conventional or automated lathe turning and boring.
There are several problems with the known core chuck 10. For example, the torque and other forces generated during the rotation of a roll of material are transmitted through the central cam 16, and ultimately through the mounting plate 12 to the rotating surface of the roll stand or similar machine. As a result, a considerable amount of torque and other loads are transmitted through the interface between the first end 22 of the central cam 16 and the opening 24 in the mounting plate 12. Because the opening 24 and the end 22 are cylindrical, the torque generated during use is transmitted only by friction and by a plurality of mounting screws 23 that secure the central cam 16 to the mounting plate 12, potentially augmented by additional conventional fasteners such as cylindrical pins. The above described connection, based upon a cylindrical pilot, tends to have critical limits of torsional capacity, which, when exceeded, cause mechanical failure with associated repair costs, production downtime costs and potentially human injury.
Accordingly, what is needed is a core chuck having an improved interface between the mounting plate and the central cam. The interface should transmit the torque and shear stresses generated during operation by non-cylindrical engagement, such that the mounting screws and associated friction holding the central cam 16 to the mounting plate 12 are not subjected to all the torque and shear loads. Such non-cylindrical engagement, permitting the central cam to serve as an integral key, further permits the screw pattern to be replaced with a single, center screw.